Innervation maintains the metabolic properties of skeletal muscle. Evidence suggests that such trophic influences of motor nerves are mediated in part by muscle activity and in part by myotrophic substance(s) carried by axonal flow. This laboratory has purified a protein from peripheral nerves which has trophic effects on muscle in culture. A primary action of this trophic protein, sciatin, appears to be the regulation of muscle protein synthesis. This study will examine the effects of this trophic protein on muscle protein turnover and compare these effects with those of muscle activity. It is hoped that this study will help to elucidate the mechanism for sciatin's trophic effect on muscle and help to explain the trophic influence of the neuron in vivo.